1. Field of the Invention
The present invention relates to a polishing method for polishing a surface to be polished of a substrate, such as a semiconductor wafer or the like, by pressing the surface to be polished of the substrate against a polishing surface of a polishing pad while supplying a polishing liquid (slurry) to the polishing surface, and moving the surface to be polished of the substrate and the polishing surface relative to each other.
2. Description of the Related Art
There have been known chemical mechanical polishing (CMP) apparatus which polish or planarize a surface to be polished of a substrate, such as a semiconductor wafer or the like, that is held by a polishing head. The CMP apparatus include a polishing pad applied to an upper surface of a polishing table and providing a polishing surface. The CMP apparatus operate by pressing the surface to be polished of the substrate against the polishing surface of the polishing pad, and rotating the polishing table and the polishing head to move the polishing surface and the surface to be polished of the substrate relative to each other while supplying a polishing liquid (slurry) to the polishing surface.
CMP technology requires that various conditions be satisfied to polish substrates at a maximum polishing rate, i.e., within a shortest period of polishing time, in order to maximize the number of substrates to be polished per unit time. To meet the requirements, CMP apparatus achieve a desired polishing rate by adjusting the pressure under which the substrate is pressed against the polishing surface of the polishing pad during polishing, the rotational speeds of the polishing head and the polishing table, and the flow rate at which the polishing liquid is supplied to the polishing surface of the polishing pad.
When a substrate is polished by such a CMP apparatus, on the other hand, heat is generated by the friction between the substrate and the polishing pad, resulting in an excessive increase in the temperature of the surface of the polishing pad and hence the temperature of a polishing interface between the polishing pad and the substrate. Such an excessive increase in the temperature may possibly prevent the CMP apparatus from achieving a maximum polishing rate. One solution is to eject a gas such as a cooling gas or the like from a gas ejecting portion such as a cooling nozzle or the like toward the surface of the polishing pad to mainly deprive the surface of the polishing pad of vaporization heat, thereby keeping normal the temperature of the surface of the polishing pad and hence the temperature of the polishing interface between the polishing pad and the substrate for a maximum polishing rate.
It has been proposed to control the surface temperature of the polishing pad in a temperature range below about 50° C., i.e., at 44° C., for thereby reducing dishing (see Japanese laid-open patent publication No. 2001-308040), and to measure the surface temperature of the polishing pad and cool the polishing pad with a cooling mechanism provided on the polishing pad, for example, depending on changes in the surface temperature of the polishing pad (see Japanese laid-open patent publication No. 2001-62706).
The applicant has proposed a polishing apparatus including a fluid ejecting mechanism for ejecting a gas, such as a compressed gas, toward the polishing surface. The fluid ejecting mechanism is controlled to maintain the polishing surface in a certain temperature distribution based on the measured temperature distribution of the polishing surface (see Japanese laid-open patent publication No. 2007-181910).